1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly to an array substrate for a liquid crystal display device and a manufacturing method thereof.
2. Discussion of the Related Art
Generally, a liquid crystal display (LCD) device includes two substrates that are spaced apart and face each other with a liquid crystal material layer interposed between the two substrates. Each of the substrates includes electrodes that face each other, wherein a voltage applied to each electrode induces an electric field between the electrodes and within the liquid crystal material layer. Alignment of the liquid crystal molecules of the liquid crystal material layer is changed by varying an intensity or direction of the applied electric field. Accordingly, the LCD device displays an image by varying light transmissivity through the liquid crystal material layer in accordance with the arrangement of the liquid crystal molecules.
FIG. 1 is a cross sectional view illustrating a liquid crystal display (LCD) device according to the related art. In FIG. 1, an LCD device has upper and lower substrates 60 and 10, which are spaced apart from and facing each other, and a liquid crystal material layer 80 interposed and sealed by a sealant 90 between the upper and lower substrates 60 and 10. The LCD device can be divided as a display region A and a non-display region B.
The upper substrate 60 includes a black matrix 62, a color filter layer 64, and a transparent common electrode 68 subsequently disposed on an interior surface thereof. The black matrix 62 includes openings having one of three sub-color filters of red (R), green (G), and blue (B). Below the black matrix 62 there is an overcoat layer 66.
The lower substrate 10, which is commonly referred to an array substrate, has a thin film transistor T having a gate electrode 22, a source electrode 34, and a drain electrode 36. On the gate electrode 22 a gate-insulating layer 24 is formed. On the gate-insulating layer 24 a silicon layer and a doped silicon layer are deposited and patterned into an active layer 26 and an ohmic contact layer 28. The source electrode 34 is connected to a data line 32 and the gate electrode 22 is connected to a gate line (not shown). The gate line and the date line 32 cross each other to define a pixel area P. On the source and drain electrodes 34 and 36 a passivation layer 40 is formed and patterned to have a drain contact hole 42 and a pad contact hole 44. A pixel electrode 52 is formed within the pixel area P to correspond to the sub-color filters (R), (G), and (B), and is electrically connected to the thin film transistor T via a drain contact hole 42. The pixel electrode 52 is made of a light transparent conductive material, such as indium-tin-oxide (ITO).
A data signal is supplied to the source electrode 34 of the thin film transistor T along a data pad 38 and the data line 32. The data pad 38 is formed at one end of the data line 32, and a data pad terminal 54 is connected to the data pad 38 via the pad contact hole 44. The data pad terminal 54 may be formed of the same material as the pixel electrode 53. The data pad 38 and the data pad terminal 54 are positioned in the non-display region B.
On each interior surface, orientation or alignment layers 72 and 74 are positioned. The orientation layers 72 and 74 have an organic material such as polyimide.
Light transmission through the liquid crystal material layer 80 is adjusted by controlling electrical and optical properties of the liquid crystal material layer 80. For example, the liquid crystal material layer 80 includes a dielectric anisotropic material having spontaneous polarization properties such that the liquid crystal molecules form a dipole when the electric field is induced. Thus, the liquid crystal molecules of the liquid crystal material layer 80 are controlled by the applied electric field. In addition, optical modulation of the liquid crystal material layer 80 is adjusted according to the arrangement of the liquid crystal molecules. Therefore, images of the LCD device are produced by controlling light transmittance of the liquid crystal material layer 80 by optical modulation of the liquid crystal material layer 80.
The manufacturing method of the array substrate will be explained. For example, when forming the gate electrode 22, a metal layer is formed by a sputtering method and patterned into the gate electrode 22 using a photolithography method. The photolithography process includes depositing a photoresist layer, exposing the photoresist layer using a patterned mask, removing the exposed portion or the non-exposed portion according to type of the photoresist material, etching the metal layer, and stripping the remaining photoresist portion. The etching method is usually chosen between a wet etching and a dry etching according to the material of being etched. The stripping process uses a stripper having an organic solvent, which is one reason of high cost.
For manufacturing the array substrate, five or six mask or lithography processes are usually adopted. Reducing the number of lithography processes has been a big task to decrease manufacturing cost.